1. Field of the Invention
The present invention relates to a resin structure and method of manufacturing it. More particularly, the present invention relates to a resin structure in which manufacturing cost is cheap and sufficient adhesive strength can be obtained and method of manufacturing it.
2. Description of the Related Art
Recently, a wiring board in which wiring of a fine pattern is provided on the surface of resin substrate is essential for a precise electronic apparatus. As the material for the resin substrate, for example, there are a printed circuit board using epoxy resin, a flexible printed circuit board on which the wiring is formed on a soft flexible film. In such a circuit board and resin substrate, the weights thereof are light, the treatments are easy, and the formations of the fine patterns are also easy. Moreover, multiple-layer structure is possible, and further it is easy to make the wiring highly dense. Thus, the above-mentioned circuit board or resin substrate can be provided in all kinds of electronic apparatuses, as the substrate of forming the wiring.
Especially in recent years, an IC chip, an LSI chip, an MPU have been provided on the board and the film formed of the above-mentioned resin materials. Accordingly, the compact cheap product has been manufactured. In the above-mentioned product, a copper wiring is typically formed on the resin substrate with plating. Then, the copper wiring and a bump electrode of the IC chip are pressed and bonded to each other, or a bonding ground of the IC chip and a bonding ground on the resin substrate are bonded to each other with wire bonding. Accordingly, an electronic circuit device is formed on the wiring substrate, and the circuit board device is completed.
To make the circuit board device further reliable, or for the sake of other reasons, the IC chip, the LSI, the MPU and other various electronic parts which are placed on the wiring substrate are sealed with seal resin. Accordingly, the influence from external environment can be shielded, which enables the high reliability of the electronic circuit to be kept. Hyper-fineness is performed on the above-mentioned wiring so that a line width thereof is about several tens of microns and also a line pitch thereof is about several tens of microns. Thus, it becomes difficult to precisely form such a hyper-fine pattern on the resin substrate.
Traditionally, this kind of laminated film has been formed by bonding copper foil to resin. As this resin layer, there is polyamide or polyimide system film. The polyamide or polyimide system film is poor in adhesive property to the copper foil. Thus, the emphasis falls on the improvement of this poor adhesive property. Various adhesives are designed and invented to improve this adhesive property. For example, the mixture of ethylene system copolymer and polyamide resin is proposed. Moreover, a mixture of cyanic acid ester system resin and butadiene system resin and acrylic acid or methacrylic acid epoxy ester is proposed. Furthermore, there are additive reaction crosslinked type of silicon rubber and the like, as material in which epoxy modification nylon has both properties of flame resistance and chemical resistance.
The polyamide or polyimide has film formation property. Thus, it is difficult to bond the polyamide or polymide to the copper foil directly and strongly. However, it has constant adhesive property. Thus, they are the resin materials very frequently used up to now. A method of forming the copper foil is referred to as a subtractive method.
A method of directly pressing and fitting a copper foil film into the surface of the resin substrate to pattern it, is performed on a non-fine pattern. However, the copper foil film can not be reduced to a sufficiently thin thickness. Moreover, the surface is not always flat. Thus, it is difficult to attain the line width of several tens of microns or the line pitch of several tens of microns.
There is another method of forming a thin film, instead of the method of forming the coil foil on the resin layer of the resin material. This is an additive method of using electroless plating, electrolytic plating or the like.
The additive method does not require the etching removal of a large amount of coil foil, as compared with the subtractive method. Moreover, in this method, the method of forming a circuit is simplified, and this is a non-polluting and resource saving type, and further the accuracy of a circuit pattern is excellent. Thus, in recent years, this has been used more and more in many cases. However, the additive method has a problem that the adhesive property between the plated circuit pattern and the printed circuit board is poor even as compared with the subtractive method. Hence, although the improvement in the above-mentioned problem is eagerly tried, a so-called photo forming method of using photo sensitive material for generating a plating core is prominent as a main inventive idea until now.
Moreover, a method of making the surface of a board rough is used overwhelmingly in many cases, as a method of improving the adhesive property between an electroless circuit pattern and the printed circuit board. In this case, adhesive is mainly coated on the surface of the board, and then the surface of the adhesive is made rough. That is, at first, this is a method of bonding to the board a plastic sheet whose surface is made rough. Secondly, diene system synthetic rubber adhesive is coated on aluminum foil on which rugged surface is formed by an alkaline zincification process, and then this coated foil and the printed circuit board are integrated with each other. Thirdly, after the integrated formation, this aluminum foil and the galvanized layer are removed to thereby form the rough surface.
In addition, there is a method of providing on a printed circuit board a coated layer having hollow holes. There is a method in which after diene system synthetic rubber system adhesive is coated on the printed circuit board, a part of the surface layer of the adhesive is cut away in a constant depth.
However, even if using the above-mentioned methods, it is very difficult to form a metal layer having the strongly adhesive force, especially the copper layer, on the so-called resin layer by the electroless plating. Moreover, since all the methods need the adhesive layer, a manufacturing cost becomes high. Thus, it is not always the that the above-mentioned methods are excellent.
There is a method of using a vacuum evaporating apparatus, a sputtering apparatus or the like, as a method in which a constantly adhesive force can be obtained between the resin layer and the metal layer. This is done through processes as shown in FIG. 1. As shown in FIG. 1, the resin substrate to form the resin layer of the laminated film is firstly prepared. Next, the metal layer serving as a base layer for planting is formed on the resin substrate by the sputtering operation, the evaporating operation or the like. Moreover, the electrolytic plating operation is performed with this metal layer as the base layer. Then, the metal layer is grown to a predetermined thickness. After that, a patterning operation, using resist and the like, is performed on the metal layer. Then, the wiring treatment is carried out with the etching operation and the like.
As another method, there is a method shown in FIG. 2. As shown in FIG. 2, at first, resin substrate is prepared, and then through-holes, via-holes and the like are formed in the resin substrate. The through-holes and the via-holes are formed with a drill. If the resin substrate is film-shaped, they are formed with a laser and the like. Next, the base layer for plating is formed with the sputtering operation or the evaporating operation, similarly to the method shown in FIG. 1. After that, the resist is used to generate a portion in which the electrolytic plating is selectively grown, namely, a portion serving as the wiring. After that, the electrolytic plating is performed, and then the resist and the base layer are removed to thereby complete the electronic circuit device in which the wiring is formed on the resin substrate.
However, in the methods shown in FIGS. 1 and 2, even if any of the sputtering operation and the evaporating operation is used to form the base layer for plating, it must be done in vacuum atmosphere. Thus, the vacuum apparatus and the like must be used although the adhesive layer and the like are not used differently from the above-mentioned methods. Hence, the facility investment becomes expensive. As a result, it is not the that this method is excellent.
By the way, a printed circuit board whose rigidity is relatively high is used in many cases, as the conventional such resin material. Especially in recent years, a multiple-layer board is used in many cases. Moreover, polyimide and the like are frequently used as a film-shaped board. Actually, other materials are limited to an extremely small number because of the problem of the adhesive strength between the material and the metal layer formed on the resin layer of the material.
As another method, a method shown in FIG. 3 is used especially in a case of a resin structure having a three-dimensional wiring. At first, catalyst that serves as the growth core for plating is mixed with resin to then form a first structure. After that, non-plated resin that does not have the growth core for plating is secondly formed, and then it is made rough, and further the electroless plating is selectively grown. However, this method also needs the process of mixing the growth core for plating with the resin and carrying out the second structure operation. The reason why the complex processes must be employed as mentioned above is that it is difficult to bond the electroless plating on the resin material under the sufficient strength.
At first, the conventional first method is as follows. When the metal layer is laminated and formed on the resin layer, the adhesive layer is used to make the surface of the adhesive layer rough to then perform the electroless plating on the rough surface of the adhesive layer. Or, the electroless plating is performed, and further the electrolytic plating is performed. In this first method, the adhesive layer must be separately formed on the resin layer, and also the surface of the adhesive layer must be made rough by using a predetermined treatment. This results in the confusingly manufacturing process and the expensive cost. Moreover, the reliability is not always high.
The second method uses the vacuum evaporating apparatus, the sputtering apparatus and the like, when forming the base layer for plating. According to this method, it is possible to form the metal layer on the resin layer under a certain adhesive strength. However, a large scale of facility, such as the vacuum apparatus and the like, must be used as mentioned above, which results in the problem that the manufacturing cost is high. In any of these methods, the adhesive strength between the resin layer and the metal layer is not always sufficient. Especially, the utilization of the fine pattern results in the problem that the stress occurring between the resin substrate and the wiring causes the wiring to be stripped from the surface of the resin substrate.
Moreover, as another method, especially in the case of the resin structure having the three-dimensional wiring, the growth core for plating is mixed with the resin, or the secondly structure operation is required. Thus, the confusion of the processes is similar to the other methods. The reason why the complex processes must be employed as mentioned above is that it is difficult to bond the electroless plating on the resin material under the sufficient strength.